Objective: We investigated whether employment as a welder with potential exposure to manganese and other substances is associated with Parkinson disease (PD), parkinsonism or related neurological disorders, or accelerates the age of onset of PD.
Methods: We selected cases and controls from 12,595 persons ever employed at three Caterpillar Inc. (CAT) plants between 1976 and 2004 with potential to make a medical insurance claim between 1998 and 2004. Cases had filed a claim for 1) PD, 2) “secondary parkinsonism”, 3) “other degenerative diseases of the basal ganglia” or 4) “essential and other specific forms of tremor”. Cases were grouped by claims: Group 1-claims 1 and 2 and Group 2-claims 1 to 4, and as study period incident (SPI) or prevalent. Each case was matched to two series of 10 controls each on date of case’s first claim, year of birth, race and sex. Series I was also matched on plant.
Results: Odds ratios (OR) and 95% confidence intervals (CI) for the variable, “ever welder in any CAT plant” were: Group 1-SPI Cases: Series I (OR = .76, CI = .26–2.19), Series II (OR = .81, CI = .29–2.25); Group 1- Prevalent Cases: Series I (OR = .82, CI = .36–1.86), Series II (OR = .97, CI = .42–2.23); Group 2- SPI Cases: Series I (OR = 1.03, CI = .57–1.87), Series II (OR = 1.21, CI = .67–2.20) Group 2-Prevalent Cases: Series I (OR = 1.02, CI = .62–1.71), Series II (OR = .86, CI = .51–1.43). Our finding of no statistically significant associations for welding employment was maintained following adjustment for potential confounding and evaluation of possible effect modification. Employment as a welder did not accelerate the age of onset of PD.
Conclusions: Our study supported the conclusion that employment as a welder is not associated with Parkinson disease, parkinsonism or a related neurological disorder.